How come horsepower tv gained a very small amount of hp off a 70mm TB on a 97 stang?

[96_4.6]

Before the tune they gained with just the bigger TB and thats the only episode I've seen with that black mustang and money is tight and I can get a mac TB for like 100-120 bucks and even if its 2hp It worth it to me theres just alyways been the pro and cons and a con is you can lose hp off it so thats why I've held off but I need some more bolt on's cause I wont be able to do a headswap or blower for a very very long time, I'm 20, live at home and I make $9.50 an hour getting a raise to 10.00 next week and I'm supposed to be saving for college hehe but keep buying car parts so I can spend small portions at a time so I dunno